Oh flipping heck!
I am extremely embarrassed at having been talking twaddle....
In my defence, I was brain dead from going round in circles with the problem.
So, effectively, I deleted a subkey which hadn't been mentioned in any of the previous articles which happened to be under the same key as one in the advice, and then I created a 'replacement' which was actually the one prescribed in the article, so that fixed the problem.
Which means that both of the machines satisfied the criteria of 'not having the key therefore create the key'.
And everything else should be ignored.
Very well spotted Boggin, thank you.
I'm now going to crawl back into a corner and put a blanket over my head until the shame dies down....